An official said four of the 10 children seized during the investigation involving Irish couples in western Mexico showed signs of sexual abuse.

Jalisco state attorney general Tomas Coronado said the children were examined by doctors, but offered no other details.

"There are four children who show signs of having been abused (sexually), perhaps not in a violent way but there are signs (of abuse)," Mr Coronado told reporters.

He said at least 11 Irish couples were involved in the case. Fifteen Irish citizens have already talked to authorities, said Lino Gonzalez, a spokesman for Jalisco state prosecutors.

The foreign couples were giving 1,200 pesos (€140) a week to the mothers since pregnancy, and paying for their medical attention, officials said.

Later the Mexican mothers would also be paid for allowing the children to stay with the couples while the purported adoption process proceeded, Mr Coronado said.

"The great majority of the people from Ireland who have given their testimony have said they thought it was part of the adoption protocol in the state to be paying and that obviously means (someone was making) a profit throughout the adoption process," he said.

Investigators are trying to determine if the Irish couples "acted in bad faith", Mr Coronado said, or were being tricked.

The Irish embassy in Mexico said it was providing consular advice to the couples involved.